German patent application P 4 118 230.8 (Le A 28 460) describes a process for isolating polymers from their solvents by addition of fluids containing carbon dioxide at temperatures of 30.degree. to 280.degree. C. and under pressures of 1 bar to 1000 bar which is characterized in that the concentration of the polymers in their solvents is between 5% by weight and 80% by weight and the fluid containing carbon dioxide consists of at least 50% by weight carbon dioxide. This process has the advantage over other processes for isolating polymers from their solvents, as described for example in U.S. Pat. No. 4,634,761, in EP 334,314-A2, in DE 3,840,293, in JP 01,168,730-A2 and in the Article by Yamamoto Koji et al. in Kagaku Kogaku Ronbunshu 15(3), 1989, pages 673-675, in that it enables large quantities of product to be quickly and simply removed without significantly exposing the product to heat.
In German patent application P 4 117 751.7 (Le A 28 369), it was additionally found that the isolation process described in P 4118230.8 (Le A 28 460) can be improved in regard to the powder formed by applying a special measure for polycarbonates. That application describes a continuous process for isolating polycarbonates from methylene chloride at temperatures of 30.degree. to 80.degree. C. in powder form with residual solvent contents below 5% by weight, characterized in that
The isolation of high-viscosity, highly heat-resistant polycarbonates by known methods presents a number of difficulties because, on account of their particular physical properties, these polycarbonates can be difficult to isolate from their organic solvents in evaporation extruders or in known precipitation processes, for example using steam or by spray drying, optionally using another solvent, such as n-heptane for example. The same also applies generally to polycarbonates of very high molecular weight and to polyester carbonates having high glass temperatures, particularly those having glass temperatures above 180.degree. C.
The same problem also affects the special polycarbonates described in DE-OS 3 832 396 (Le A 26 344) which are based on diphenols having special cycloaliphatic lateral groups, more particularly polycarbonates containing more than 40 mol-% of these diphenols.
In addition, it is important in the process to establish isolation conditions which protect the nozzles used against blockage and back-pressure. This applies quite generally to polycarbonates.